Wireless communication systems can include a network of one or more base stations to communicate with one or more user equipment (UE) such as fixed and mobile wireless communication devices, mobile phones, or laptop computers with wireless communication cards. Base stations are spatially distributed to provide radio coverage in a geographic service area that is divided into cells. A UE that is located within a base station's cell of coverage area is generally registered with the base station. The UE and the base station communicate with each other via radio signal. The base station is called the serving base station of the UE and the cell associated with the base station is called the serving cell of the UE.
In some wireless networks, cells of different coverage sizes may be deployed to improve cell coverage or to offload traffic. For example, in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), small cells (e.g., pico cells, relay cells, or femto cells) may be deployed with overlaid macro cells. A network including large cells (e.g., macro cells) as well as small cells (e.g., pico cells, relay cells, femto cells) may be referred to as a heterogeneous network. A UE in the heterogeneous network may move in a large geographical area which may trigger a handover procedure and result in changing of the UE's serving cells.